Machines such as, for example, dozers, motor graders, wheel loaders, wheel tractor scrapers, and other types of heavy equipment are used to perform a variety of tasks. Autonomously and semi-autonomously controlled machines are capable of operating with little or no human input by relying on information received from various machine systems. For example, based on machine movement input, terrain input, and/or machine operational input, a machine can be controlled to remotely and/or automatically complete a programmed task. By receiving appropriate feedback from each of the different machine systems during performance of the task, continuous adjustments to machine operation can be made that help to ensure precision and safety in completion of the task. In order to do so, however, the information provided by the different machine systems should be accurate and reliable. The heading (also referred to as “yaw”), roll, and pitch of the machine are parameters whose accuracy may be important for control and positioning of the machine.
Conventional machines typically utilize a positioning system to determine various operating parameters such as velocity, pitch rate, yaw rate, roll rate, etc. The positioning system relies on Global Navigation Satellite System (GNSS) data along with data from an Inertial Measurement Unit (IMU) to calculate the yaw, roll, and pitch of the machine. As an example, a 4-degree of freedom (4 DOF) IMU may be utilized to determine the attitude (orientation) of the machine. A 4 DOF IMU consists of 3 accelerometers and a single gyroscope that measures an angular rate of the machine, for example, a pitch rate of the machine.
A reliable indication of the pitch rate and pitch of the machine is desirable in a machine that includes an earth moving implement such as a blade or a bucket. If the machine controller receives an accurate pitch or pitch rate measurement, the controller may be able to keep the earth moving implement stable so that it may be easily controlled by the operator of the machine. While the gyroscope in the 4 DOF IMU provides a reliable indicator of the pitch rate relative to the inertial-body reference frame (“body reference frame”) of the machine, the gyroscope in the 4 DOF IMU does not provide a reliable indication of the pitch rate relative to the gravity earth-tangent reference frame (“gravity reference frame”). The body reference frame is a reference frame that describes movement relative to itself (the body of the system) in space. The gravity reference frame is a reference frame that describes the position, orientation, and movement relative to the earth's surface.
The gyroscope's inability to provide a reliable indication of the pitch rate relative to the gravity reference frame may be illustrated by considering an example of a tractor positioned on a hill pitched 45 degrees with 0 degrees of roll. If the tractor now turns (yaws) 180 degrees, the tractor is pitched negative 45 degrees with 0 degrees of roll with respect to the earth's surface. However, the gyroscope will not detect this change in pitch because the gyroscope measures the change in pitch with respect to the machine's body and not with respect to the earth's surface. An inaccurate reading of the pitch of the machine may result in the controller not being able to keep the earth moving implement stable or maintain a desired grade for the earth moving implement.
An exemplary system used to control a blade of a machine is disclosed in U.S. Patent Publication No. 2009/0069987 to Omelchenko et al. (“Omelchenko”) that published on Mar. 12, 2009. The Omelchenko publication provides a system that controls a blade elevation and blade slope angle. The Omelchenko system compensates tangential and centripetal accelerations arising from circular motions of a machine. For compensating the tangential and centripetal accelerations, the Omelchenko system uses rotation matrices that denote rotation between a blade frame (a reference frame fixed with respect to the blade) and a vehicle frame (a reference frame fixed with respect to the dozer body).
Although the Omelchenko system may be useful in controlling the blade of a machine, the Omelchenko system may not provide an adequate correction for the angular rates that are determined in the body reference frame. For example, the Omelchenko system may not properly convert a pitch rate from the body reference frame to the gravity reference frame.
The implement controller of the present disclosure is directed toward solving one or more of the problems set forth above and/or other problems of the prior art.